Biochemical compounds such as glucose, cholesterol, urea nitrogen, uric acid, bilirubin, ammonia, hemoglobin, neutral fat, lactic acid, fructosylamino acid, and L-glycerolphosphoric acid are contained in various biological liquids or body fluids such as whole blood, plasma, serum, urine, lymph, and pulpal liquid. The quantitative analysis of the biochemical compound (i.e., analyte) in body fluids is of great value for diagnosis of patients suffering from various diseases.
Previously, the quantitative analysis of the analytes have been performed by a wet method or a dry method. The wet method generally comprises a color formation reaction between the analyte and a color-forming reagent or in the presence of the analyte in an aqueous medium. The dry method generally employs a strip or a multilayer analytical element containing a color-forming reagent. Each of these methods has each advantageous feature and therefore both are widely employed in diagnosis of patients who possibly suffer from various diseases. However, both methods have disadvantageous features in that it is not easy to obtain the test results quickly because the color formation reaction is involved, and further they show a relatively low sensitivity in analyzing an extremely small amount of analyte.
In order to obtain the test results more quickly and to analyze an extremely small amount of analyte with an increased sensitivity, and enzyme sensor such as glucose sensor has been developed. The analytical system of the glucose sensor comprises the step of oxidizing the target glucose with glucose oxidase to produce gluconic acid and hydrogen peroxide and the step of detecting the amount of the produced hydrogen peroxide by a hydrogen peroxide electrode to give an electric signal corresponding to the amount of the hydrogen peroxide. This system is disadvantageous from the view point of complicated apparatuses involved.
In Chemical Letters pp. 989-990 (1998), a report entitled "Enhanced Electron Transfer from Glucose Oxidase to DNA-Immobilized Electrode aided by Ferrocenyl Naphthalene Diimide, a Threading Intercalator" is published. The author includes the present inventors. The report discloses that a ferrocene-modified 1,4,5,8-naphthalene-tetracarboxydiimide bound to double stranded DNA by a threading intercalation mode, enhanced the electron transfer between glucose oxidase and a DNA-immobilized electrode. This report, however, does not teach that the discovery may be utilized in analytical methods.
Recently, it has been desired to provide a method of quantitative analysis of analytes in body fluids which gives the analytical results more easily and more quickly using a simple apparatus.